Endocrine Abstracts

Background: Recommendations for the diagnosis of phaeochromocytoma are based on individual institutional experience but have traditionally advocated concurrent measurement of urine and plasma catecholamines. However, reports of phaeochromocytoma presenting with normal catecholamines suggest that this practice is insufficiently sensitive. In phaeochromocytoma there is an increased output of metadrenaline metabolites with a disproprtionate increase in the unconjugated form and evidence suggests that urinary metadrenalines may provide a better test than urinary catecholamines. Moreover, recent evidence suggests that unconjugated plasma metanephrines provide a sensitive test. As liquid chromatography allows the measurement of urinary fractionated metadrenalines, we have evaluated a novel approach, measuring urinary free normetadrenaline and urinary free metadrenaline independently using the ASTED system.

Methods: We performed a retrospective analysis of 155 patients in whom 24 hour urinary total catecholamines, VMA, and free metadrenalines were measured between September 1999 and February 2003. 91 (59%) patients in this group also had plasma catecholamines measured. 21 patients had histologically confirmed phaeochromocytoma. Of the sub-group with plasma catecholamine measurements 18 patients had phaeochromocytoma. True negatives were defined by normal imaging, low clinical suspicion, identification of an alternative diagnosis and no occurrence after phaeochromocytoma was excluded.

Results: Sensitivity: urinary free normetadrenaline(fnma) or free metadrenaline(fma) 100%; urinary noradrenaline(NA) or adrenaline(AD) 81%; urinary VMA 76.2%; plasma catecholamines 72.2%. Specificity: urinary VMA 97.8%, (NA) or adrenaline(AD) 97%, Urinary fnma or fma 94.8% ; plasma catecholamines 90.4%. Positive predictive value: urinary NA or AD 89.5%; urinary VMA 84.2%; urinary fnma or fma 75% and plasma catecholamines 65%. Negative predictive value: urinary free fnma or fma 100%; urinary VMA 96.3%; urinary NA or AD 95.6%; and plasma catecholamines 93.3%.

Conclusion: Urinary free metadrenalines provide a highly sensitive and specific test. We suggest that they may represent the best diagnostic biochemical test for phaeochromocytoma and in excluding the disorder.